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Domed Dine Was The King Of The Head Butt

June 29, 2011

Researchers, studying the heads of modern animals and one of the world’s best dinosaur fossils (Stegoceras), have found that the bony anatomy of the dinosaur skull was better at protecting the brain than in any modern head-butter.

Scans and computer modeling suggest that the pachycephalosaur domes of Stegoceras — a small, two-legged dinosaur that browsed leaves and berries in forests of the Late Cretaceous — were built to fend off rivals by delivering vicious head butts. Results of the study appear in the journal PLoS One.

“Pachycephalosaur domes are weird structures not exactly like anything in modern animals. We wanted to test the controversial idea that the domes were good for head butting,” said Dr. Eric Snively, University of Calgary alumnus and post-doctoral researcher in biomedical engineering at Ohio University, a co-author of the study.

“Were pachycephalosaurs more likely just showing off their domes like peacocks with their tails, or were they also cracking their heads together like musk oxen?” he asked.

“Our analyses are the closest we can get to observing their behavior. In a way, we can get “Ëœinside their heads’ by colliding them together virtually. We combined anatomical and engineering analyses of all these animals for a pretty thorough approach,” Snively said in a statement. “We looked at the actual tissue types in the skulls and heads of the animals.”

The bony anatomy of the Stegoceras head would have been quite effective at absorbing heavy blows, and better able to protect the animal’s brain than that of any living creature that shows this type of behavior in today’s animal kingdom.

Head butting is a form of male-to-male competition for access to females, according to Dr. Jessica Theodor, co-author and associate professor in the biological sciences department at the University of Calgary. “It’s pretty clear that although the bones are arranged differently in the Stegoceras, it could easily withstand the kinds of forces that have been measured for the living animals that engage in head butting.”

“The Stegoceras skull is almost like an enhanced motorcycle helmet. It has a stiff outer shell and a compliant layer beneath, and then another really stiff layer over the brain,” Snively told The Guardian.

X-rays of the skulls of modern animals, including giraffes and llamas, which do not engage in cranial combat, shows that these animals would most likely sustain sever brain trauma if they were to butt heads, according to the study.

The researchers used a hospital CT scanner and collision simulation software to probe the role of the thick, bony domes that characterize pachycephalosaurs. Another theory suggests the domes were used solely as a sexual display.

The scans showed that both Stegoceras and modern head-butting animals have relatively large neck muscles and a dense skull dome of cortical bone above a spongier layer of cancellous bone. The living animal whose skull most closely resembled Stegoceras was the common duiker, a small antelope that is native to sub-Saharan Africa.

The Stegoceras skull used in the study was 3.5 inches think, though some skulls have been up to 8 inches thick.

“It is clear that although the bones are arranged differently in the Stegoceras, it could easily withstand the kinds of forces that have been measured for the living animals that engage in head-butting,” said Theodor. 

Image Caption: Stegoceras skeletons, Royal Tyrrell Museum, Alberta, Canada. Credit: Sebastian Bergmann/Wikipedia (CC BY-SA 2.0) 

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